1. Field of the Invention
The present invention relates to the field of content distribution in an IPTV (Internet Protocol Television) network. In particular, the present invention provides an system and method for delivering IPTV content over an existing Internet Protocol (IP) backbone using Generic Routing Encapsulation (GRE) tunneling.
2. Description of the Related Art
Internet Protocol Television (IPTV) is a system for transmitting television content over high-speed Internet connections. Conventional television content is usually sent to television sets by way of either cable, satellite, or through the air in the form of analog or digital signals. IPTV is similar to VoIP (Voice over Internet Protocol) for telephonic signals, in that it includes breaking a signal into packets at a source, sending the data (e.g. video programming) across the Internet using a suitable protocol, and reassembling the packets at a destination.
In IPTV applications, national content and programming are generally accumulated at one or two places, commonly referred to as Super Hub Offices (SHOs). This content is distributed from the SHOs to multiple Video Hub Offices (VHOs). Local channels and programming content are added at the VHO. IPTV programs are commonly stored as video at the VHOs and sent out to local customers who receive the signal at computers or at special set-top boxes attached to television sets, for instance.
There are generally several methods available for use in data distribution. Unicasting describes communication in which a piece of information is sent from one (source) point to another (destination) point, where a point may refer to a router, for example. If there are multiple destination points, then the information is transmitted from the source point multiple times, once for each destination point. Protocols that operate through unicasting include http, smtp, ftp and telnet. Multicasting describes communication in which a packet of information is sent from one source point to many destination points without having to duplicate the packet at the source point for each recipient. Multicasting is not the same as broadcasting on the Internet or on a LAN. Broadcast data are sent to every possible receiver, while multicast packets are sent only to receivers that want them.
Packets distributed using multicasting are replicated in the network by routers enabled with a multicast routing protocol, such as Protocol Independent Multicasting (PIM). PIM is an adaptive method of multicasting that responds to changes in network conditions and to changes in distributions of destination points. PIM finds a multicast path between source and destinations. PIM provides method of joining routers and an ability to recover from router failure. The multicast router determines which direction is upstream (towards the source) and which is downstream. A PIM adjacency is a relationship between selected neighboring routers and end nodes for the purpose of exchanging routing information
Routers executing a multicast routing protocol, such as PIM, maintain forwarding tables. These routers may separate routing and forwarding functionality. Non-Stop Forwarding (NSF) is a generic term for the ability of a router to carry on forwarding packets even though the device responsible for the calculation of the routing and forwarding tables may be temporarily inoperable. NSF fundamentally relies on the separation of routing and forwarding functionality within the router.
Several network architectures are currently available in the prior art for distributing TV content from the SHOs to the VHOs. FIG. 1 (Prior Art) shows a Synchronous Optical Network (SONET) ring architecture. In a SONET ring, digital signals travel over a fiber optic cable. The two SONET rings 110 and 120 shown in FIG. 1 provide connections from SHOs 102 and 103 to VHOs 104, 106, and 108. Each SHO and each VHO connects to the ring at a Point-of-Presence (POP) 122 via an add/drop multiplexer (ADM) 140 capable of extracting and inserting lower-rate signals from a higher-rate multiplexed signal without completely de-multiplexing the signal. A single SONET ring may be dedicated to a single SHO, such as SONET ring 110 is dedicated to SHO 102 and SONET ring 120 is dedicated to SHO 103. Although a SONET ring may be very reliable, it is also extremely costly.
FIG. 2 (Prior Art) illustrates a native multicast architecture for IPTV content distribution over a national Internet Protocol (IP) backbone. In the native IP-multicast architecture of FIG. 2, routers in the SHO 202 and in the VHOs 204 establish PIM adjacencies with the routers 210 in the national IP backbone 225. Although the architecture of FIG. 2 delivers multicast traffic efficiently, it is not reliable for TV service and requires an upgrade in order to be implemented over a national IP backbone. Although the national IP backbone supports NSF for unicast traffic, it does not support NSF for multicast traffic. Thus, the architecture of FIG. 2 is generally unavailable for use in broadcast TV distribution.
The present invention addresses efficiency and reliability issues as well as problems with scaling issues inherent in previous architectures.